I. Field of the Invention
The present invention relates generally to open waveguide antennas, and more particularly to a flared trough waveguide antenna suitable for use at millimeter wave frequencies.
II. Description of the Related Art
The Federal Communications Commission is currently considering various proposals for redesignation of the 27.5 to 29.5 GHz frequency band for use by so-called Local Multipoint Distribution Services (LMDS). Developers of LMDS have proposed to offer broadband two-way video communications, including video distribution, teleconferencing, and data services using a cellular system design to establish communications links with subscribers. In this regard the of LMDS proponents seek to provide viable alternatives to the services offered by cable operators and local exchange carriers. It is anticipated that the cellular-like capabilities of LMDS will enable diverse services to be offered within the same region.
An LMDS system typically includes a plurality of hub transceivers used to create small cells, generally less than six miles diameter. Each hub transceiver transmits to subscriber locations and receives subscriber transmissions on a return path. Because of the typically small cell size, and arrangement in a typical cellular pattern, a very high level of frequency reuse is possible. The potential for high frequency reuse, in combination with the availability of broadband millimeter spectrum, results in the proposed LMDS systems possessing sufficient capacity to serve as wireless alternatives to existing telephone and cable providers.
The ability of LMDS to join services traditionally provided by separate communications service providers (e.g., cable television, telephony, video communications, data transfers, and interactive transactions) has created international interest. A number of countries have licensed LMDS technology on an experimental or permanent basis in the 28 GHz band. LMDS is believed to offer the prospect for modern wireless telephone systems, video distribution and the like to developing countries which do not have a wireline or cable infrastructure.
In order to facilitate a desired level of sectorization within the cells of an LMDS system, the hub or base station antenna system must be capable of providing antenna beam patterns of relatively high directivity. Moreover, the sidelobes of the beam associated with each sector should also be at least partially suppressed as a means of reducing interference between adjacent cell sectors. Unfortunately, it has hitherto been difficult to develop millimeter wave antenna systems capable of achieving such objectives in a manner which is both economical and highly power efficient. Although relatively efficient millimeter wave antenna architectures have been described, the complexity of many such architectures has resulted in comparatively high production and development costs. On the other hand, inexpensive planar array antennas (e.g., microstrip printed patch arrays) may provide the requisite directivity, but are typically inefficient due to the utilization of lossy feed networks in the distribution of power to the array radiators.
Accordingly, there exists a need for a millimeter wave antenna of relatively high directivity suitable for incorporation in LMDS and other millimeter wave communication system.